Statement - 案例

以下是示例，它使用以下三个查询以及开始和结束语句 -

• boolean execute(String SQL) :如果可以检索ResultSet对象，则返回布尔值true; 否则，它返回false。 使用此方法执行SQL DDL语句或需要使用真正动态的SQL时。

• int executeUpdate(String SQL) :返回执行SQL语句所影响的行数。 使用此方法执行SQL语句，您希望它们受到多个行的影响 - 例如，INSERT，UPDATE或DELETE语句。

• ResultSet executeQuery(String SQL) :返回ResultSet对象。 当您希望获得结果集时，请使用此方法，就像使用SELECT语句一样。

此示例代码是基于前面章节中完成的环境和数据库设置编写的。

复制并通过JDBCExample.java中的以下示例，编译并运行如下 -

//STEP 1. Import required packages
import java.sql.*;
public class JDBCExample {
   // JDBC driver name and database URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
   static final String DB_URL = "jdbc:mysql://localhost/EMP";
   //  Database credentials
   static final String USER = "username";
   static final String PASS = "password";
   public static void main(String[] args) {
   Connection conn = null;
   Statement stmt = null;
   try{
      //STEP 2: Register JDBC driver
      Class.forName("com.mysql.jdbc.Driver");
      //STEP 3: Open a connection
      System.out.println("Connecting to database...");
      conn = DriverManager.getConnection(DB_URL,USER,PASS);
      //STEP 4: Execute a query
      System.out.println("Creating statement...");
      stmt = conn.createStatement();
      String sql = "UPDATE Employees set age=30 WHERE id=103";
      // Let us check if it returns a true Result Set or not.
      Boolean ret = stmt.execute(sql);
      System.out.println("Return value is : " + ret.toString() );
      // Let us update age of the record with ID = 103;
      int rows = stmt.executeUpdate(sql);
      System.out.println("Rows impacted : " + rows );
      // Let us select all the records and display them.
      sql = "SELECT id, first, last, age FROM Employees";
      ResultSet rs = stmt.executeQuery(sql);
      //STEP 5: Extract data from result set
      while(rs.next()){
         //Retrieve by column name
         int id  = rs.getInt("id");
         int age = rs.getInt("age");
         String first = rs.getString("first");
         String last = rs.getString("last");
         //Display values
         System.out.print("ID: " + id);
         System.out.print(", Age: " + age);
         System.out.print(", First: " + first);
         System.out.println(", Last: " + last);
      }
      //STEP 6: Clean-up environment
      rs.close();
      stmt.close();
      conn.close();
   }catch(SQLException se){
      //Handle errors for JDBC
      se.printStackTrace();
   }catch(Exception e){
      //Handle errors for Class.forName
      e.printStackTrace();
   }finally{
      //finally block used to close resources
      try{
         if(stmt!=null)
            stmt.close();
      }catch(SQLException se2){
      }// nothing we can do
      try{
         if(conn!=null)
            conn.close();
      }catch(SQLException se){
         se.printStackTrace();
      }//end finally try
   }//end try
   System.out.println("Goodbye!");
}//end main
}//end JDBCExample

现在让我们编译上面的例子如下 -

C:\>javac JDBCExample.java
C:\>

运行JDBCExample ，它会产生以下结果 -

C:\>java JDBCExample
Connecting to database...
Creating statement...
Return value is : false
Rows impacted : 1
ID: 100, Age: 18, First: Zara, Last: Ali
ID: 101, Age: 25, First: Mahnaz, Last: Fatma
ID: 102, Age: 30, First: Zaid, Last: Khan
ID: 103, Age: 30, First: Sumit, Last: Mittal
Goodbye!
C:\>